Agencies plan for furloughs as the congressional duel over spending cuts intensifies.

Reporting from Washington — As a Republican-led marathon to slash spending extended late into Friday night, federal officials began developing plans to furlough workers, and prospects grew for a government shutdown in as little as two weeks.

GOP leaders in the House considered dozens of amendments to a proposal that would cut more than $60 billion from federal spending over the next seven months. Amendments approved Friday would dismantle the landmark healthcare law and halt funding for Planned Parenthood, the family-planning organization.

With funding set to expire March 4, House Minority Leader Nancy Pelosi (D-San Francisco) offered a proposal late Friday to extend spending at current levels through March 31 to give Congress more time to seek a compromise. But Republican leaders rejected it, saying they would not agree to a freeze without cuts.

The developments reflected the rising stakes in the GOP's efforts to orchestrate perhaps the largest reduction in federal spending ever attempted in one legislative measure. President Obama vows to veto the bill in the unlikely event that the Senate, in Democratic control, concurs on the cuts.

"The quickest way to achieve savings, if you have to do it very fast, is cutting off paychecks," said Robert Bixby, a budget hawk and executive director of the Concord Coalition who favors a slower approach. "It's the easiest way to do it."

The spending cut package is historic in its size as well as its scope. It is many times the size of the cuts passed by the House in 1995, when Republicans led by then-Speaker Newt Gingrich sought to reduce nondefense discretionary spending by about 5%. By comparison, the package debated Friday would cut about 15%.

President Clinton vetoed the 1995 bill, setting up the standoff that led to a series of government shutdowns months later.

Both chambers are taking a weeklong recess next week in the midst of the emerging showdown that will sharply limit the time available to avoid a potential funding crisis.

When the two sides return to work, they will have five days at most — and probably fewer, given the usual legislative workweek — to resolve deep differences and put a new spending plan in place for the remainder of the year.

Even the option of a stopgap measure that could temporarily fund the government for a few weeks until the impasse can be resolved now appears off the table as Republican leaders refuse to bend.

Several federal agencies, including the Department of Homeland Security, the Internal Revenue Service and the Social Security Administration, warned that the historic cuts approved by House Republicans would have adverse effects if enacted. They said those could include job losses and a backlog in their ability to provide services.

Senators agree on the need for cuts, but the Democratic majority characterizes the GOP-backed bill as too extreme. Senate Majority Leader Harry Reid (D-Nev.) wants to freeze spending at current levels, a proposal House Republicans mock as inadequate.

Each side has tried to position the other to take the blame if the standoff results in shuttered government offices affecting Americans across the nation.

"We don't want to do that; we hope our Republican colleagues don't want to do it," said Rep. Steny H. Hoyer (D-Md.), a House Democratic leader. "But if the posture they take is 'our way or no way,' it's possible that will happen."

Feelings have hardened during the weeklong debate. Earlier, House Speaker John A. Boehner (R-Ohio) dismissed concerns that the spending cuts would eliminate programs that help employ Americans, saying that if jobs are lost, "so be it."

As the debate over this year's budget stretched on for another day and night, the budget-cutting exercise helped define both parties.

The day's events also revealed a persistent divide within the ranks of House Republicans. Boehner has allowed a freewheeling debate. But the exercise in democracy also exposed deep rifts between his emboldened conservative wing and other members.

The conservative flank of the GOP lost one pivotal vote to reduce government funding to 2008 levels, as many of them wanted. Veteran Republican leaders admonished the leading budget cutters for pushing the additional $22 billion in cuts, saying they went too far.

The chairman of the House Appropriations Committee, Rep. Harold Rogers (R-Ky.), said the conservatives' proposal "hits everything indiscriminately in a heavy-handed way."

"We were elected to make choices, not run on autopilot," he said.

Republicans approved a measure offered by Rep. Mike Pence (R-Ind.) that would prohibit federal funds for Planned Parenthood. The group already is prohibited from using federal grants in providing abortion services.

A full-scale attack on the healthcare overhaul law advanced as Republicans approved several measures that prevented the law from taking effect. Republicans have pledged to dismantle the healthcare law, a key demand of the "tea party" movement.

In a series of votes Friday, Republicans approved measures to block funding, including one that would bar salaries for government workers implementing the law.

The healthcare votes came as the nonpartisan Congressional Budget Office said in an updated assessment that repealing the healthcare law would actually drive up federal deficits by $210 billion by 2021 and leave 22 million more Americans without health insurance.